Professor Wiilliam Happer is the Cyrus Fogg Brackett Professor of Physics at America's prestigious Princeton University, and ackowledged as a world authority in his field. In this briefing paper for Britain's Global Warming Policy Foundation, Professor Happer explains in scientifically valid but layman-friendly terms why carbon dioxide is neither a "pollutant" nor a cause of undesirable levels of "global warming". This is a must-read for everyone interested in the topic, or worried about the future of planet Earth.